Resistance spot welding (RSW) is used for the fabrication of sheet metal assemblies. The process is used to join low carbon steel components by applying a potential across two electrodes connected to the respective components. High-strength low-alloy steel, stainless steel, nickel, aluminum, titanium and copper alloys are also frequently spot welded. RSW is used in a variety of applications including automotive welding of the bodies and chassis of automobiles, trucks, trailers, buses, mobile homes, motor homes and recreational vehicles, as well as for joining cabinets, office furniture, appliances and many other products.
Resistance spot welding can be performed at high speeds and is particularly useful for automated high rate production assemblies. However, due to the complexity of the basic process, RSW potentially produces inconsistent weld quality. Previous methods of quality control testing have traditionally revolved around destructive testing to physically inspect the weld integrity. Such destructive testing completely destroys the workpiece, and wastes both resources and materials, especially in large volume production operations. Pry or “chisel” tests which distort the metal are also used. Although ultrasonic non-destructive testing of RSW is known, previously it has not been used with great success due to requirements for highly trained operators, manual dexterity, weld material dependences, and cost.
Thus, ensuring weld quality has been and remains a major challenge and goal. There is a need for an ultrasonic testing apparatus that provides a fast, reliable, high quality method of inspecting small target areas, which is neither cost prohibitive nor operator dependent.